This invention relates to an improvement in the process for graphitizing long, regularly shaped carbon electrode columns consisting of formed and carbonized coke aggregate and pitch.
Traditionally, graphite electrodes have been manufactured by heating formed carbon columns to the temperature necessary to properly develop the most desirable properties by a method described in U.S. Pat. No. 1,357,290 - Kemmer. In this method the carbon columns are heated by passing an electric current from massive electrodes through a packed mass containing the columns. The columns are positioned on a bed of carbon particles with a spacing therebetween and packed well with a mixture of coke particles called "resistor coke", the columns lying perpendicular to the electric field set up by the massive electrodes. The resistance to passage of electric current afforded by the carbon is responsible for the heating.
Another method of heating carbon columns comprises passing electric current directly through one or more coaxially aligned columns, positioned in abutting relationship so that there is an electrical connection between them, in a lengthwise manner, the current being supplied by electrodes placed at each end of the column or group of columns. Several problems inherent in the utilization of this method of heating are (1) adapting the current-supplying electrodes to move as the columns expand in length during heating (that is, accomodating the linear expansion); (2) providing the proper electrical connection between the current-supplying electrodes and the carbon column or the ends of a group of columns; and (3) providing sufficient force to reduce resistance between the current-supplying electrodes and the columns.
If more than one carbon column is placed lengthwise in the path of current, a serious additional problem is providing a packing of some appropriate electrically conductive material between the ends of the columns. The packing material must be of the same or similar electrical resistance as the carbon, and it must be at least somewhat deformable. It is this problem to which this invention is directed.